Empirical Analysis of Passive Microwave Observations from Bbaskara-II SAMIR and Remote Sensing of Atmospheric Water Vapor and Liquid Water

Abstract

Empirical and statistical techniques have been used to examine a large dataset of near-nadir brightness temperature measurements at 19, 22 and 31 GHz over tropical oceans from the Satellite Microwave Radiometer (SAMIR) system onboard the Bhaskara-II satellite. Told water vapor data from NOAA-7 satellite have been used in an empirical correlation analysis in conjunction with the near-coincident SAMIR data to establish statistical relationships between brightness temperature and total water vapor under cloud-free conditions. Bi-spectral distributions of the SAMIR data have been analyzed through a partially supervised cluster analysis technique to separate the liquid water contaminated data based on their spectral response. From this analysis, approximate threshold brightness temperature values for the three SAMIR channels have been fixed, above which cloud liquid water effect dominates. In order to verify these threshold values, limited SAMIR data related to cloudy conditions have been examined in conjunction with the NOAA-7 satellite cloud imageries. A reasonable qualitative spatial correlation has been found between the cloudy regions, as identified on the basis of the SAMIR threshold values, and the satellite cloud observations. Finally, using a simple scheme an approximate regression equation has been derived for estimating atmospheric liquid water content over ocean from the SAMIR data. Liquid water estimates for a few cases have been made to illustrate the simplified approach.